Using in or on for vehicles depends on which type of vehicle you are talking about.

Use in for private or small vehicles.

Examples:

• ​Margaret arrived at the party in a limousine.

• We went for a joy ride in Lucy’s car.

• Put the picnic basket in the truck.

• ​Julian rode to the market in my land-rover.

• I saw a couple riding up the river in a canoe.
  

​Use on for large vehicles and public transportation.

Examples:

• Everyone on the bus ignored the loud preacher.

• We’ll have to find some space for our luggage on the plane.

• I saw some football fans on the train.

• Agnes found two suitcases on the boat.
  

Use on for bicycles and motorcycles.

Examples:

• We arrived on Ama’s motorbike.

• ​How can five people ride on one bicycle?